Acer benefited from strong shipments during the back to school season, as prices for laptops fell and netbook shipments gained momentum, said Jay Chou, research manager at IDC.

Dell has not embraced low cost netbooks as enthusiastically as Acer, Chou said. Acer benefitted more from the competitive pricing environment for laptops and netbooks.

Acer ended the quarter with 14 percent of the market, compared to Dell's 12.7 percent. Both companies trailed HP, which retained its spot as the world's top PC vendor. HP held 20.2 percent of the market after shipping 15.79 million PCs, a year over year growth rate of 9.3 percent.

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HP is stronger in retail sales than Dell, which helped it generate stronger back to school sales.

Dell is stronger in sales to businesses, and it could rebound during a corporate PC refresh cycle that could happen in 2010, Chou said. Until then, Dell may struggle to keep up with competitors in unit shipments. The company saw solid growth in emerging markets, IDC noted, which was a positive sign.

Ever since Dell lost its market share lead, founder and CEO Michael Dell has insisted he is more concerned with profits. "If we wanted [market share], we'd go and sell a whole bunch of netbooks," he said in a recent earnings call. Netbooks carry lower profit margins than full-fledged PCs.

Lenovo recorded strong growth of 18.2 percent, giving it the fourth place spot with PC shipments of 6.99 million. Toshiba was fifth, with shipments growing 6.9 percent to 4.04 million.

"The continued strength of both the US and worldwide PC business in the face of difficult economic environments underscores the value that both consumer and corporate buyers place on PCs," Bob O'Donnell, vice president for clients and displays at IDC, said in a statement.

PC shipments in the US grew by 2.5 percent during the third quarter, while shipments in Asia Pacific "grew nicely," IDC said. Shipments in Japan declined by a double digit percentage as consumer and corporate spending remained weak. Shipments also declined in EMEA, IDC said.